1. Field of the Invention
This invention relates to the field of elastic couplings which are used in suspensions, in particular the suspensions of vehicle wheels and engines. More particularly, it is an application of hydraulic and/or pneumatic damping to said elastic coupling when it is used as a suspension fastener between the rod of a vehicle shock absorber and the body of the vehicle.
2. Background Information
In any suspension system of a conventional drive train, when a spring provides the vertical flexibility, the pivoting is made possible by additional contact of a cup on a thrust ball bearing which transits the permanent load to the body. This additional fastening, like that of the shock absorber rod with which it is coaxial, requires a filtering which limits the vibrations transmitted via the spring. This function is very commonly performed by parts which are made of vulcanized rubber and which are intimately bonded to the cup and to the corresponding fastening ring.
The elastic parts which perform these functions have been the subject of numerous improvements, including the device disclosed by EP-A-0 249 369 (General Motors), which improves exclusively the elastic coupling between the shock absorber rod and the chassis, by limiting the dynamic deformations by means of thrust washers, while the end-of-stroke forces on a shock absorber stop must be exerted by means of another rigid cup, although this arrangement does not absorb the permanent load.
In an opposite manner, FR-A-2 583 126 (Honda) discloses a device which incorporates a roller thrust bearing to carry the permanent load of the suspension spring, but provides a good filtering of the acoustical vibrations only for the shock absorber rod, by means of a "vibration neutralizer".
On the other hand, the device which is disclosed in DE-A-3 034 743 (Continental) combines, in one complex part, permanent support--via a roller thrust bearing--of the suspension spring as well as the elastic spring where the connecting force is exerted, in dynamic alternation, between the shock absorber rod and the support on the body. In this design, the dynamic end-of stroke forces are exerted on the fastening of the shock absorber rod, as a result of the presence of a rubber stop, and not via the roller bearing, which supports a load which is not subject to a great deal of variation, because it is modulated exclusively by the flexibility of the spring, even in the event of rapid deflections.
In a similar manner, FR-A-2 563 302 (Volvo) discloses a device, called a MacPherson strut mount, in which a small space makes possible a short free displacement between stops, inside an upper fastening of the shock absorber rod, which also supports the permanent load of the spring.
Improvements which introduce a hydraulic damping at the upper fastening point of a shock absorber always relate to the attachment of the shock absorber rod and absorb the dynamic end-of-stroke force as a result of the impact of the tube of the shock absorber on an appropriate elastomer stop.
This method of improving vibratory comfort under the effect of wheel loads is disclosed in FR-A-2 587 774 and FR-A-2 623 866 (Tokai Rubber). These improvements are still applied exclusively to the connection between the shock absorber rod and the body, or a similar application. The device combines in one single part two opposite chambers connected by a liquid passage coiled around their outside diameter, a passage which is very long and has a significant cross section, and produces a major inertial effect, while the viscosity of the liquid contained in the passage does not act on the displacements.
These devices, the inertial effects of which block the deformation if the shock absorber exerts rapid forces, nevertheless make possible deflections in the event of slower movements thanks to the guidance provided either by a ring which, in the first document cited above, is concentric with the fastening, the elastomer of which is prestressed to improve its fatigue behavior, or, in the second document cited above, by an annular part with radial deflection.
The design of these devices is therefore very complex, although their single, very limited function is that of an elastic fastening point. The performance of the other functions also requires a similar level of complexity, to guarantee the uniformity of the level of quality required with regard to the filtering of noise and vibrations in the connections between the chassis and an automobile suspension system, as well as the gradual action required for the damping.
The analysis of the prior art shows that none of the devices of the prior art performs all of these functions satisfactorily or with simplicity, i.e. the improvement of the damping of vibrations of the vehicle's drive train and the gradual damping of the forces as a function of the displacement of the connection between the shock absorber rod and the vehicle chassis, while reducing the forces transmitted to said chassis by the vehicle drive train, while suppressing the impacts introduced, at the limits of deflection, by the displacement limiting devices, which most frequently generate annoyances caused by excessive noise, and by reducing the friction, which generates wear of the elastomer limit stops and thereby induces alterations of the performance of the elastic coupling.
Nor do any of the techniques used in the prior art make it possible to obtain, with a single device using simple means, a modulation not only of the dynamic characteristics, but also a modulation of the static rigidity and the damping action.
The invention is therefore a variable elastic coupling assembly, forming a shock absorber attachment and a filtering block, between the rod of a vehicle shock absorber and a structure to be damped. It consists of rigid annular armatures which are intimately bonded to a connecting assembly made of elastomer to delimit a closed space, containing a fluid used to fill the closed space, said variable elastic coupling assembly being rigidly linked on one hand to the rod of the shock absorber by means of an internal lower armature and an internal upper armature, and on the other hand to the structure to be damped by means of at least one upper armature.
The invention is characterized by the fact that the closed space is delimited by an assembly of upper annular armatures and/or an assembly of lower annular armatures, so that it can be completely sealed with respect to its external environment by the installation of plugs after filling, and by the fact that a modulation of the static and dynamic characteristics can be obtained by varying the composition of the fluid used to fill the closed space and/or of the volume of said closed space which, interacting with the elastomer compound connecting assembly, makes it possible on one hand to adapt the relative displacements of the components of the upper and lower annular armature assemblies, and of said elastomer compound connecting assembly, and on the other hand to filter the vibrations as a function of the requirements for a gradual damping action.